Weight loss, in the context of medicine, health, or physical fitness, refers to a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue or lean mass, namely bone mineral deposits, muscle, tendon, and other connective tissue. Weight loss can either occur unintentionally due to malnourishment or an underlying disease or arise from a conscious effort to improve an actual or perceived overweight or obese state. "Unexplained" weight loss that is not caused by reduction in calorific intake or exercise is called cachexia and may be a symptom of a serious medical condition. Intentional weight loss is commonly referred to as slimming.

Intentional

Intentional weight loss is the loss of total body mass as a result of efforts to improve fitness and health, or to change appearance through slimming. Weight loss in individuals who are overweight or obese can reduce health risks,[1] increase fitness,[2] and may delay the onset of diabetes.[1] It could reduce pain and increase movement in people with osteoarthritis of the knee.[2] Weight loss can lead to a reduction in hypertension (high blood pressure), however whether this reduces hypertension-related harm is unclear.[1][not in citation given]

Weight loss occurs when the body is expending more energy in work and metabolism than it is absorbing from food or other nutrients. It will then use stored reserves from fat or muscle, gradually leading to weight loss. For athletes seeking to improve performance or to meet required weight classification for participation in a sport, it is not uncommon to seek additional weight loss even if they are already at their ideal body weight. Others may be driven to lose weight to achieve an appearance they consider more attractive. However, being underweight is associated with health risks such as difficulty fighting off infection, osteoporosis, decreased muscle strength, trouble regulating body temperature and even increased risk of death.[3]

Low-calorie diets are also referred to as balanced percentage diets. Due to their minimal detrimental effects, these types of diets are most commonly recommended by nutritionists. In addition to restricting calorie intake, a balanced diet also regulates macronutrient consumption. From the total number of allotted daily calories, it is recommended that 55% should come from carbohydrates, 15% from protein, and 30% from fats with no more than 10% of total fat coming from saturated forms.[citation needed] For instance, a recommended 1,200 calorie diet would supply about 660 calories from carbohydrates, 180 from protein, and 360 from fat. Some studies suggest that increased consumption of protein can help ease hunger pangs associated with reduced caloric intake by increasing the feeling of satiety.[4]Calorie restriction in this way has many long-term benefits. After reaching the desired body weight, the calories consumed per day may be increased gradually, without exceeding 2,000 net (i.e. derived by subtracting calories burned by physical activity from calories consumed). Combined with increased physical activity, low-calorie diets are thought to be most effective long-term, unlike crash diets, which can achieve short-term results, at best. Physical activity could greatly enhance the efficiency of a diet. The healthiest weight loss regimen, therefore, is one that consists of a balanced diet and moderate physical activity.[citation needed]

Though hypothesized that supplementation of vitamin D may help, studies do not support this.[7] The majority of dieters regain weight over the long term.[8]

According to the Dietary Guidelines for Americans those who achieve and manage a healthy weight do so most successfully by being careful to consume just enough calories to meet their needs, and being physically active.[9] According to the U.S. Food and Drug Administration (FDA), healthy individuals seeking to maintain their weight should consume 2,000 calories (8.4 MJ) per day.[citation needed]

Techniques

The least intrusive weight loss methods, and those most often recommended, are adjustments to eating patterns and increased physical activity, generally in the form of exercise. The World Health Organization recommended that people combine a reduction of processed foods high in saturated fats, sugar and salt[10] and caloric content of the diet with an increase in physical activity.[11]

An increase in fiber intake is also recommended for regulating bowel movements. Other methods of weight loss include use of drugs and supplements that decrease appetite, block fat absorption, or reduce stomach volume. Bariatric surgery may be indicated in cases of severe obesity. Two common bariatric surgical procedures are gastric bypass and gastric banding.[12] Both can be effective at limiting the intake of food energy by reducing the size of the stomach, but as with any surgical procedure both come with their own risks[13] that should be considered in consultation with a physician. Dietary supplements, though widely used, are not considered a healthy option for weight loss.[14] Many are available, but very few are effective in the long term.[15]

Virtual gastric band uses hypnosis to make the brain think the stomach is smaller than it really is and hence lower the amount of food ingested. This brings as a consequence weight reduction. This method is complemented with psychological treatment for anxiety management and with hypnopedia. Research has been conducted into the use of hypnosis as a weight management alternative.[16][17][18][19] In 1996 a study found that cognitive-behavioral therapy (CBT) was more effective for weight reduction if reinforced with hypnosis.[17]Acceptance and Commitment Therapy ACT, a mindfulness approach to weight loss, has also in the last few years been demonstrating its usefulness.[20]

Permanent weight loss

In order for weight loss to be permanent, changes in diet and lifestyle must be permanent as well. Short-term dieting has not been shown to produce either long term weight loss or better health, and may even be counterproductive.[21]

In 2008 between US$33 billion and $55 billion was spent annually in the US on weight-loss products and services, including medical procedures and pharmaceuticals, with weight-loss centers taking between 6 and 12 percent of total annual expenditure. Over $1.6 billion a year was spent on weight-loss supplements. About 70 percent of Americans' dieting attempts are of a self-help nature.[23][24]

Unintentional

Characteristics

Unintentional weight loss may result from loss of body fats, loss of body fluids, muscle atrophy, or even a combination of these.[25][26] It is generally regarded as a medical problem when at least 10% of a person's body weight has been lost in six months[25][27] or 5% in the last month.[28] Another criterion used for assessing weight that is too low is the body mass index (BMI).[29] However, even lesser amounts of weight loss can be a cause for serious concern in a frail elderly person.[30]

Unintentional weight loss can occur because of an inadequately nutritious diet relative to a person's energy needs (generally called malnutrition). Disease processes, changes in metabolism, hormonal changes, medications or other treatments, disease- or treatment-related dietary changes, or reduced appetite associated with a disease or treatment can also cause unintentional weight loss.[25][26][27][31][32][33] Poor nutrient utilization can lead to weight loss, and can be caused by fistulae in the gastrointestinal tract, diarrhea, drug-nutrient interaction, enzyme depletion and muscle atrophy.[27]

Continuing weight loss may deteriorate into wasting, a vaguely defined condition called cachexia.[30] Cachexia differs from starvation in part because it involves a systemic inflammatory response.[30] It is associated with poorer outcomes.[25][30][31] In the advanced stages of progressive disease, metabolism can change so that they lose weight even when they are getting what is normally regarded as adequate nutrition and the body cannot compensate. This leads to a condition called anorexia cachexia syndrome (ACS) and additional nutrition or supplementation is unlikely to help.[27] Symptoms of weight loss from ACS include severe weight loss from muscle rather than body fat, loss of appetite and feeling full after eating small amounts, nausea, anemia, weakness and fatigue.[27]

Serious weight loss may reduce quality of life, impair treatment effectiveness or recovery, worsen disease processes and be a risk factor for high mortality rates.[25][30] Malnutrition can affect every function of the human body, from the cells to the most complex body functions, including:[29]

In addition, malnutrition can lead to vitamin and other deficiencies and to inactivity, which in turn may pre-dispose to other problems, such as pressure sores.[29]

Unintentional weight loss can be the characteristic leading to diagnosis of diseases such as cancer[25] and type 1 diabetes.[34]

In the UK, up to 5% of the general population is underweight, but more than 10% of those with lung or gastrointestinal diseases and who have recently had surgery.[29] According to data in the UK using the Malnutrition Universal Screening Tool ('MUST'), which incorporates unintentional weight loss, more than 10% of the population over the age of 65 is at risk of malnutrition.[29] A high proportion (10-60%) of hospital patients are also at risk, along with a similar proportion in care homes.[29]

Causes

Disease-related

Disease-related malnutrition can be considered in four categories:[29]

Problem

Cause

Impaired intake

Poor appetite can be a direct symptom of an illness, or an illness could make eating painful or induce nausea. Illness can also cause food aversion.

Inability to eat can result from: diminished consciousness or confusion, or physical problems affecting the arm or hands, swallowing or chewing. Eating restrictions may also be imposed as part of treatment or investigations. Lack of food can result from: poverty, difficulty in shopping or cooking, and poor quality meals.

Impaired digestion &/or absorption

This can result from conditions that affect the digestive system.

Altered requirements

Changes to metabolic demands can be caused by illness, surgery and organ dysfunction.

Excess nutrient losses

Losses from the gastrointestinal can occur because of symptoms such as vomiting or diarrhea, as well as fistulae and stomas. There can also be losses from drains, including nasogastric tubes.

Other losses: Conditions such as burns can be associated with losses such as skin exudates.

Weight loss issues related to specific diseases include:

As chronic obstructive pulmonary disease (COPD) advances, about 35% of patients experience severe weight loss called pulmonary cachexia, including diminished muscle mass.[31] Around 25% experience moderate to severe weight loss, and most others have some weight loss.[31] Greater weight loss is associated with poorer prognosis.[31] Theories about contributing factors include appetite loss related to reduced activity, additional energy required for breathing, and the difficulty of eating with dyspnea (labored breathing).[31]

Cancer, a very common and sometimes fatal cause of unexplained (idiopathic) weight loss. About one-third of unintentional weight loss cases are secondary to malignancy. Cancers to suspect in patients with unexplained weight loss include gastrointestinal, prostate, hepatobiliary (hepatocellular carcinoma, pancreatic cancer), ovarian, hematologic or lung malignancies.

People with HIV often experience weight loss, and it is associated with poorer outcomes.[35] Wasting syndrome is an AIDS-defining condition.[35]

Therapy-related

Medical treatment can directly or indirectly cause weight loss, impairing treatment effectiveness and recovery that can lead to further weight loss in a vicious cycle.[25]

Many patients will be in pain and have a loss of appetite after surgery.[25] Part of the body's response to surgery is to direct energy to wound healing, which increases the body's overall energy requirements.[25] Surgery affects nutritional status indirectly, particularly during the recovery period, as it can interfere with wound healing and other aspects of recovery.[25][29] Surgery directly affects nutritional status if a procedure permanently alters the digestive system.[25]Enteral nutrition (tube feeding) is often needed.[25] However a policy of 'nil by mouth' for all gastrointestinal surgery has not been shown to benefit, with some suggestion it might hinder recovery.[37]

Early post-operative nutrition is a part of Enhanced Recovery After Surgery protocols.[38] These protocols also include carbohydrate loading in the 24 hours before surgery, but earlier nutritional interventions have not been shown to have a significant impact.[38]

Some medications can cause weight loss,[39] while others can cause weight gain.[40][41]

Social conditions

Social conditions such as poverty, social isolation and inability to get or prepare preferred foods can cause unintentional weight loss, and this may be particularly common in older people.[42] Nutrient intake can also be affected by culture, family and belief systems.[27] Ill-fitting dentures and other dental or oral health problems can also affect adequacy of nutrition.[27]

Loss of hope, status or social contact and spiritual distress can cause depression, which may be associated with reduced nutrition, as can fatigue.[27]